Circuit arrangement for braking a vehicle

ABSTRACT

A circuit arrangement for the combined net and resistance braking of an electrically driven vehicle is fed via a pair of lines from a direct current power system. A capacitor is connected across the pair of lines, as is a resistive braking circuit composed of a series arrangement of a braking resistor and a controllable switch. A voltage regulating circuit having its input connected in parallel with the capacitor and its output coupled to the control input of the controllable switch is arranged to develop a control signal upon the occurrence of a voltage across the capacitor which exceeds slightly the rated voltage of the pair of lines.

United States ate n9 Putz Feb. 6, 1973 CIRCUIT ARRANGEMENT FOR BRAKING AVEHICLE lnventor: Ulrich Putz, Berlin 41, Germany Assignee: LicentiaPatent Verwaltungs- G.m.b.'H., Frankfurt, Germany Filed: March 20, 1972App]. No.: 236,323

Foreign Application Priority Data March 20,1971 Germany ..P 21 14 121.9

US. Cl ..307/9 Int. Cl. ..ll-l02g 3/00 Field of Search ..105/61; 307/10R, 106, 149,

, References Cited v, UNITED STATES PATENTS 2/1968 Hubbard ..307/10 RPrimary ExaminerHcrman J. Hohauscr Alt0rney-George H. Spencer et al.

57 ABSTRACT A circuit arrangement for the combined net and resistancebraking of an electrically driven vehicle is fed via a pair of linesfrom a direct current power system. A capacitor is connected across thepair of lines, as is 1 a resistive braking circuit composed of a seriesarrangement of a braking resistor and a controllable switch. A voltageregulating circuit having its input connected in parallel with thecapacitor and its output coupled to the control input of thecontrollable switch is arranged to develop a control signal upon theoccurrence of a voltage across the capacitor which exceeds slightly therated voltage of the pair of lines.

13 Claims, 3 Drawing Figures w ill CIRCUIT ARRANGEMENT FOR BRAKING AVEHICLE BACKGROUND OF THE INVENTION This invention relates to a circuitarrangement for the combined net and resistance braking of electricallydriven vehicles.

The present invention relates, more particularly, to a circuitarrangement for the combined net and resistance braking of electricallydriven vehicles which are fed from a direct current power system via apair of higher power than starting because it is the practice to' brakethe drive motors from full speed with torques which lie in the order ofmagnitude of the starting moment and, in some instances, torques whichare even higher. Fully electrical net braking is thus possible only if,at the time of braking, a number of other loads are capable of using thecorresponding power supplied to the mains from the braked vehicle or ifthe substations are able to store such power and to feed the storedpower back into the mains. The feedback capability of direct currentsubstations, however,'has not heretofore been investigated .since norequirement existed for feedback capability before the introduction ofcontrolled semiconductor rectifiers. Moreover, the voltage The foregoingobjects, as well as others which will become clear from the text below,are accomplished in accordance with the present invention by providing acircuit arrangement for the combined net and resistance braking of anelectrically driven vehicle which is fed via a pair of lines from adirect current power system. A capacitor is connected across the pair oflines, which may consist of a trolley wire and a ground connection. Aresistive braking circuit is connected across the pair of lines. Theresistive braking circuit in- -cludes a braking resistor and acontrollable switch connected in series with one another. A voltageregulating circuit having its inputconnected across the capacitor dropsacross the mains would be changed in polarity so that an excess voltagewould occur at the vehicle itself, which would endanger the entireelectrical system. This canbe overcome by using a braking resistance inwhich the full kinetic energy of the vehicle is converted to heat assoon as the net, i.e. the system power network, can no longer absorb allof the energy. In order to be able to at least somewhat'utilize theadvantage of the net braking, the amount of power fed back is adaptedto. the needs'of other available loads, only the excess energy beingconverted into heat in the braking resistance. Known electrically drivenvehicles with mixed net and resistance brakes, however, exhibit, interalia,

.. the following drawbacks:

l. The control of the direct current switch must be different whenoperating in its net braking mode than when operating in its resistancebraking mode so that with combined-net and resistance braking highdemands are placed on the current control circuits and the switch. Forexample, during the transition from full resistance braking to full netbraking, the controller used must be actuated over almost its fullrange.

2. In the above-mentioned instance, the intermittently connected brakeresistance cannot be used for excess voltage protection.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a circuit arrangement for combined net and resistance brakingwhich is of uncomplicated construction.

It is another object of the present invention to provide a circuitarrangement for combined net and resistance braking which also functionsas a protection circuit against excess voltage levels.

is provided. The output of the voltage regulator is coupled to thecontrol input of the controllable switch for supplying a control signalthereto which is produced whenever the voltage across the capacitorexceeds slightly the rated voltage of the pair of lines.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of acircuit arrangement, according to the present invention, for thecombined net and resistance braking of a vehicle driven by rangementshown in FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIG. I, acircuit arrangement for the combined net and resistance braking of anelectrically driven vehicle (not illustrated) includes a buffercapacitor 5 connected across a pair of lines 10 and l 1, one terminal ofthe capacitor 5 being connected directly to the line 11, shown asground, and the other terminal being connected to the line 10,illustrated as a trolley wire, via a choke 6.

A resistive circuit, generally designated by the numeral l, is connecteddirectly in parallel with the capacitor 5. The resistive circuit 1includes a braking resistor 2 and a controllable semiconductor switch 3which are connected in series with each other. The control electrode ofthe controllable semiconductor switch 3 is connected to the output of avoltage regulating circuit 4.

The input of the voltage regulating circuit 4 is connected directlyacross the capacitor 5. During operation, the voltage regulator circuit4 senses the voltage across the capacitor 5 and produces a controlsignal, as its output signal to the control electrode of thecontrollable semiconductor switch 3, whenever the voltage across thecapacitor 5 exceeds slightly the'rated voltage of the pair of lines 10,ll.

The voltage regulator circuit 4- may take a number of different forms.For example, the voltage regulator circuit 4 may bea conventionalregulating control circuit which produces a direct current signalwhenever the voltage across the capacitor 5 exceeds the rated linevoltage by a predetermined value. The direct current signal isamplified, by a conventional amplifying circuit forming part of thevoltage regulator circuit 4, and is applied to the control electrode ofthe controllable semiconductor switch to place it in its conductivestate, resulting in the dissipation of energy in the braking resistor 2so long as the controllable semiconductor switch 3 remains in itsconductive state. Whenever the voltage across the capacitor falls belowthe value slightly above the rated voltage of the pair of lines 10, l l,the voltage regulator circuit 4 responds by abruptly terminating orchanging the level of its direct current signal, the amplifying circuitwithin the voltage regulator amplifies the signal which results in theproduction of a turn-off pulse which places the controllablesemiconductor switch 3 in its non-conductive state terminating theresistance braking. As an alternative construction, the voltageregulator circuit 4 may be a pulse producing circuit which produces atrain of pulses of a given repetition rate and varying pulse width inresponse to its input sensing that the voltage across the capacitor 5exceeds slightly the rated voltage of the pair of lines 10, 11, thepulse width being substantially directly proportional to the extent thevoltage across the capacitor 5 exceeds the rated line voltage. Thepulses of varying width are amplified, as before, and the amplifiedpulses used to turn the controllable semiconductor switch on and off.Thus, the duty cycle of the controllable semiconductor switch 3 isvaried as a function of the extent the voltage across the capacitor 5exceeds a given voltage slightly above the rated voltage of the pair oflines 10, 11.

The working of both regulating systems is explained on principle byHeumann/Stumpe in the book Thyristoren, Teubner-Verlag, Stuttgart 1969,pages 167 to 170. Furthermore there is described one regulating systemabove mentioned by Swoboda in Elektro-Technik 47 (1965) pages 23lto 233,FIG. 3, and the other regulating system by Hengsberger, Putz, Vetters inAEG-Mitteilungen," 1964, pages 438 to 442, especially FIGS. 7 and 8.

' A direct current motor 12 is connected in series with thepair oflines10, 11 via a d.c.-chopper circuit 7 and the choke 6, terminals a and bof the d.c.-chopper being effectively connected across the capacitor 5.As shown more in detail in FIG. 3 the d.c.-chopper 7 is connected to thedirect current motor 12. The control circuit 14 provides an enablingsignal to the d.c.-chopper 7 for placing it in its conductive statewhenever an operator elects town the motor 12 by energizing the controlcircuit .14. The control circuit 14 supplies pulses to turn thed.c.-chopper 7 on and off, respectively.

Referring to FIG. 3, which shows more detailed the interior circuit 7 ofFIG. 1, a pairof terminals a, b, which correspond to the terminals a, bshown in FIG. 1 are connected to a semiconductor-device 7 as shown inFIG. 1 containing the thyristor 20 with its selfcommuwhich produces atrain of pulses of a given repetition rate and the d.c.-chopper 7 isplaced in its conductive state at a set repetition rate, it isadvantageous to provide that the given repetition rate be a fixed wholenumber multiple of the set repetition rate. The repetition rate of thecurrent through the braking resistor 2, for best operation, should lieabove the highest possible resonant frequency of a circuit formed by thebuffer capacitor 5, the choke 6 and the inductance of the net, includingline 10. It is to be appreciated that the effective net inductancedepends on the distance the vehicle is from the power stations feedingthe net.

A complete embodiment of a motor control circuit for use in the dc.motor embodiment of FIG. 1 is shown in FIG. 3 of the above mentionedmagazine Elektro-Technik 47," 1965, pages 231 to 233 and in the FIGS. 7and 8 of the magazineffAEG-Mitteilungen, 1964, pages 438 to 442. i

The resistance value of the braking i resistor 2 is so dimensioned that,upon the occurrence of the full brake power and no acceptance capabilityof the net, the voltage which occurs across the capacitor 5 lies onlyslightly above the normal net voltage. If the vehicle is braked withless energy orifthe riet is capable of absorbing energy, thecontrollable semiconductor switch 3 is not placed in its conductivestate by the voltage regulator circuit 4 which isc'orrriected inparallel with the resistive circuit 1 and the buffer capacitor 5.Semiconductor switch 3 consequently only conducts during periodsrequired to convert electrical energy into heat so as to maintain theset voltage value. In the borderline case, the braking resistor 2 iseffectively disconnected from the buffer capacitor 5 when the netabsorption capability is high, i.e. when the controllable semiconductorswitch 3 blocks. Since the resistive braking circuit 1 is switched on bythe voltage regulating circuit 4 to different degrees during driving aswell as braking, the circuit arrangement serves as an excess voltageprotection during events which endanger the electrical system of thevehicle. Such events may occur, 7

for example, from the resonating of the LC filter formed by the inputchock 6, the inductance of the net including the wire 10 and the buffercapacitor 5 or by braking of a vehicle in the vicinity.

As can be seen from the foregoing, the braking resistor 2 with the aidof the controllable semiconductor switch 3 can be effected in two ways:

1. The voltage regulating circuit 4 may operate as a two-point regulatorin that it senses the instant value of the voltage across the buffercapacitor 5 and regulates the value of the voltage appearing across thebuffer capacitor 5 by the two point method, or

2. The voltage regulating circuit 4 may control the controllablesemiconductor switch 3 in such a manner that this switch switches thebraking resistor 2 into and out of connection across the buffercapacitor 5 at a constant repetition rate but with variable connectionperiods.

The first arrangement is less expensive and is particularly well suitedfor monitorable net conditions while the second arrangement isadvantageous where a change in the net inductance (variable distancefrom the substation) can change the resonant frequency of the filterformed by the inputchoke 6, the net inductance and the buffer capacitor5. In this case the repetition rate of the current through the brakingresistor 2 must lie at an appropriate distance above the highestpossible resonant frequency as pointed out above.

Referring now to FIG. 2, a pair of terminals a and b, which correspondto the terminals a,b, shown in FIG. I, are shown connected to a combinedD.C. to A.C./A.C. to D.C. converter 8. The converter 8, in turn, isconnected to a three-phase alternating current motor 117. In order tooperate the alternating current motor 17 and to provide combinedresistance and net braking, the pair of terminals a and b are connectedacross the voltage regulating circuit shown in FIG. 1.

In operation, the converter 8 converts direct current to three-phasealternating current which is supplied to the alternating current motor17 during running. During braking, the converter 8 converts three-phasealternating current from the alternating current motor 17 into directcurrent, the direct current being fed-to the circuit arrangement shownto the left of the pair of terminals a,b, shown in FIG. 1.

A controllable converter circuit suitable for use as the circuit 8 inFIG. 2 is shown in the U.S. Pat. No. 3,399,336.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

Iclaim:

l. A circuit arrangement for the combined net and resistance braking ofan electrically driven vehicle fed via a pair of lines from a directcurrent power system comprising, in combination:

a motor means for driving the vehicle,

a controllable switching circuit means for coupling I said motor meansacross said pair of lines,

a capacitive means coupled across said pair of lines;

a resistive braking circuit connected in parallel with said capacitivemeans, said resistive braking circuit including a resistance means and acontrollable switch means connected in series with one another, saidcontrollable switch means having a control input;

voltage regulating circuit means having an input means and an outputmeans, said input means being connected in parallel with said capacitivemeans and responsive to the voltage appearing across said capacitivemeans for developing a control signal across its output means upon theoccurrence of a voltage across said capacitive means which exceedsslightly the rated voltage of said pair of lines; and

means for coupling said output means of said voltage regulating circuitmeans to said control input of said controllable switching means formaintaining the voltage across said capacitive means substantiallyconstant.

2. A circuit as defined in claim 1 wherein said controllable switchmeans is a semiconductor switch.

3. A circuit as defined in claim 1 wherein said voltage regulatingcircuit means is a pulse producing circuit responsive to the voltageacrosssaid capacitive means and which produces as the control signalpulses of varying width, the width of the pulses depending on thevoltage appearing across said capacitive means in excess of a voltagelevel slightly above the rated voltage of said pair of lines.

4. A circuit as defined in claim 1 wherein said voltage regulatingcircuit means is a regulator circuit which produces as the controlsignal a direct voltage signal whenever the voltage across saidcapacitive means exceeds a voltage level slightly above the ratedvoltage of said pair of lines.

5. A circuit as defined in claim 3 wherein said pulse producing circuitproduces pulses having a given repetition rate.

6. A circuit as defined in claim 1 wherein said motor means is a directcurrent motor and wherein said controllable switching circuit means is athyristor including its selfcommutating circuit means for couplingenergy from the direct current motor means to said capacitive means andsaid pair of lines during braking and for coupling energy from said pairof lines to said direct current motor means during running.

7. A circuit as defined in claim 6 further comprising circuit meanscoupled to said controllable switching circuit means for intermittentlyactivating said controllable switching circuit means at a set repetitionrate whereby said direct current motor means is coupled across said pairof lines and said capacitive means at the set repetition rate. I

8. A circuit as defined in claim 5 wherein said motor means is a directcurrent motor, and said controllable switching circuit means is athyristor including its selfcommutating circuit means; and furthercomprising circuit means coupled to said controllable switching circuitmeans for intermittently activating said controllable switching circuitmeans at a set repetition rate, said given repetition rate being a fixedand whole number multiple of said set rate.

9. A circuit as defined in claim 1 wherein said motor means is analternating motor means and wherein said controllable switching circuitmeans includes converter means for converting direct current from saidpair of lines into alternating current as input to said alternatingcurrent motor means during running and for converting alternatingcurrent from said alternating current motor means into direct current asinput to said pair of lines and said capacitive means during braking.

it). A circuit as defined inclaim 9 further comprising circuit meanscoupled to said converter means for intermittently activating saidconverter means at a set repetition rate during braking.

ll 1. A circuit as defined in claim 10 wherein said voltage regulatingcircuit means is a pulse producing circuit responsive to the voltageacross said capacitive means and which produces as the control signalpulses of given repetition rate, said given repetition rate being afixed whole number multiple of said set repetition rate.

12. A circuit as defined in claim 111 wherein said pulse producingcircuit produces as the control signal pulses of varying width, thewidth of the pulses depending on the voltage appearing across saidcapacitive means in excess of a voltage level slightly above the ratedvoltage of said pair of lines.

113. A circuit as defined in claim 1 wherein said resistive brakingcircuit and said voltage regulator means are effective as operativelyarranged to provide excess voltage protection for said motor means.

1. A circuit arrangement for the combined net and resistance braking ofan electrically driven vehicle fed via a pair of lines from a directcurrent power system comprising, in combination: a motor means fordriving the vehicle, a controllable switching circuit means for couplingsaid motor means across said pair of lines, a capacitive means coupledacross said pair of lines; a resistive braking circuit connected inparallel with said capacitive means, said resistive braking circuitincluding a resistance means and a controllable switch means connectedin series with one another, said controllable switch means having acontrol input; voltage regulating circuit means having an input meansand an output means, said input means being connected in parallel withsaid capacitive means and responsive to the voltage appearing acrosssaid capacitive means for developing a control signal across its outputmeans upon the occurrence of a voltage across said capacitive meanswhich exceeds slightly the rated voltage of said pair of lines; andmeans for coupling said output means of said voltage regulating circuitmeans to said control input of said controllable switching means formaintaining the voltage across said capacitive means substantiallyconstant.
 1. A circuit arrangement for the combined net and resistancebraking of an electrically driven vehicle fed via a pair of lines from adirect current power system comprising, in combination: a motor meansfor driving the vehicle, a controllable switching circuit means forcoupling said motor means across said pair of lines, a capacitive meanscoupled across said pair of lines; a resistive braking circuit connectedin parallel with said capacitive means, said resistive braking circuitincluding a resistance means and a controllable switch means connectedin series with one another, said controllable switch means having acontrol input; voltage regulating circuit means having an input meansand an output means, said input means being connected in parallel withsaid capacitive means and responsive to the voltage appearing acrosssaid capacitive means for developing a control signal across its outputmeans upon the occurrence of a voltage across said capacitive meanswhich exceeds slightly the rated voltage of said pair of lines; andmeans for coupling said output means of said voltage regulating circuitmeans to said control input of said controllable switching means formaintaining the voltage across said capacitive means substantiallyconstant.
 2. A circuit as defined in claim 1 wherein said controllableswitch means is a semiconductor switch.
 3. A circuit as defined in claim1 wherein said voltage regulating circuit means is a pulse producingcircuit responsive to the voltage across said capacitive means and whichproduces as the control signal pulses of varying width, the width of thepulses depending on the voltage appearing across said capacitive meansin excess of a voltage level slightly above the rated voltage of saidpair of lines.
 4. A circuit as defined in claim 1 wherein said voltageregulating circuit means is a regulator circuit which produces as thecontrol signal a direct voltage signal whenever the voltage across saidcapacitive means exceeds a voltage level slightly above the ratedvoltage of said pair of lines.
 5. A circuit as defined in claim 3wherein said pulse producing circuit produces pulses having a givenrepetition rate.
 6. A circuit as defined in claim 1 wherein said motormeans is a direct current motor and wherein said controllable switchingcircuit means is a thyristor including its selfcommutating circuit meansfor coupling energy from the direct current motor means to saidcapacitive means and said pair of lines during braking and for couplingenergy from said pair of lines to said direct current motor means duringrunning.
 7. A circuit as defined in claim 6 further comprising circuitmeans coupled to said controllable switching circuit means forintermittently activating said controllable switching circuit means at aset repetition rate whereby said direct current motor means is coupledacross said pair of lines and said capacitive means at the setrepetition rate.
 8. A circuit as defined in claim 5 wherein said motormeans is a direct current motor, and said controllable switching circuitmeans is a thyristor including its selfcommutating circuit means; andfurther comprising circuit means coupled to said controllable switchingcircuit means for intermittently activating said controllable switchingcircuit means at a set repetition rate, said given repetition rate beinga fixed and whole number multiple of said set rate.
 9. A circuit asdefined in claim 1 wherein said motor means is an alternating motormeans and wherein said controllable switching circuit means includesconverter means for converting direct current from said pair of linesinto alternating current as input to said alternating current motormeans during running and for converting alternating current from saidalternating current motor means into direct current as input to saidpair of liNes and said capacitive means during braking.
 10. A circuit asdefined in claim 9 further comprising circuit means coupled to saidconverter means for intermittently activating said converter means at aset repetition rate during braking.
 11. A circuit as defined in claim 10wherein said voltage regulating circuit means is a pulse producingcircuit responsive to the voltage across said capacitive means and whichproduces as the control signal pulses of given repetition rate, saidgiven repetition rate being a fixed whole number multiple of said setrepetition rate.
 12. A circuit as defined in claim 11 wherein said pulseproducing circuit produces as the control signal pulses of varyingwidth, the width of the pulses depending on the voltage appearing acrosssaid capacitive means in excess of a voltage level slightly above therated voltage of said pair of lines.